1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to methods and apparatus for assembling semiconductor chip packages.
2. Description of the Related Art
Many current integrated circuits are formed as multiple die on a common silicon wafer. After the basic process steps to form the circuits on the die are complete, the individual die are cut from the wafer. The cut die are then usually mounted to structures, such as circuit boards, or packaged in some form of enclosure.
One frequently-used package consists of a substrate upon which a die is mounted. The upper surface of the substrate includes electrical interconnects. The die is manufactured with a plurality of bond pads. A collection of solder bumps are provided between the bond pads of the die and substrate interconnects to establish ohmic contact. An underfill material is deposited between the die and the substrate to act as a cushion and an adhesive to hold the die. After the die is mounted to the substrate, a lid is attached to the substrate to cover the die. Some conventional integrated circuits, such as microprocessors, generate sizeable quantities of heat that must be ferried away to avoid device shutdown or damage. For these devices, the lid serves as both a protective cover and a heat transfer pathway.
The attachment of a lid to a die substrate involves a complex choreography of steps. A thermal interface material must be applied to the die. An adhesive must be applied to the substrate and cured in such a way that does not produce unwanted irregularities in the thickness or wetting of the thermal interface material. The lid must be attached to the substrate so that the tilt of the lid relative to the die is within acceptable tolerances. High tilt can lead to nonuniformities in thermal interface material thickness, which can produce poor heat transfer characteristics.
One conventional apparatus for assembling packages is the model LAS64 manufactured by Dai-Ichi Seiko. This conventional machine includes several processing stations that perform various stages of lid-to-substrate assembly. A feature common to these processing stations is the capability to handle only a single package size. However, many semiconductor devices, particularly those newer devices incorporating large or multiple die, are made in a variety of sizes. Separate machines are needed for each size.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.